The Application Of Time-Domain Phase-Inversion Symmetric Method In CDMA

CDMA belongs to the Direct Sequence Spread Spectrum Technology. DSSS denoted by DS, obtains strong anti-jamming ability by increasing the bandwidth. However, because the adjacent time slot noise has a certain relevance, we can not get the desired spreading gain. In order to take full advantage of the limited spectrum resources to get stronger anti-jamming capability, People use a variety of techniques. For example, the orthogonal code, quasi-orthogonal codes, chaotic spread spectrum sequences etc. But they can not overcome the adverse effects with the noise correlation.My mentor proposed Phase-Inversion Symmetric Method. It depressed noise by using the relativity of noise, changed the unfavorable factors into favorable factors, greatly improved the system signal-to-noise ratio.It has been patented in China.This paper studied the PISM in time-domain, realized the combination of PISM and DS, improved the signal-to-noise ratio of the system with the same band width. Main tasks are as follows:(1) The correlation analysis of the band limited noise.The correlation of the adjacent time slot noise was simulated by using MATLAB software, the results showed that the adjacent time slot noise was correlative, and time slot smaller, the correlation stronger. The data of adjacent time slot man-made noise and natural noise correlation was tested actually by using the oscilloscope, the experimental results showed that the correlation coefficient of man-made noise was greater than the correlation coefficient of the natural noise. Many tests results showed that whether natural or man-made noise, the adjacent time slot noise was positive correlation, correlation coefficient ofρ＞0.(2) Introducing the basic principle of PISM and carrying on the theory analysis and simulation about anti-noise performance of time domain PISM.Through the theoretical analysis of the PISM, we obtained the PISM system signal-to-noise ratio gain formula is GPISM=2/(1-ρ). The relationship of the PISM and shannon theorem was analysesed. The applicable scope of PISM was obtained. The anti-noise performance between the time domain PISM and the existing diversity technology was compared. Based on the theory analysis of PISM feasibility of time domain, I got the time domain PISM system signal-to-noise ratio gain GPISM≈3.1 under the band limited noise conditions. For different code piece rate and time slot, the anti-noise performance of PISM was simulated by using MATLAB software.(3) combining PISM with DS and building the PISM-DSS model, testing the anti-interference ability of PISM-DSS for gaussian white noise, narrowband interference, comb interference and broadband interference. The curcuits of coder and decoder of PISM were designed by using Multisim software.The results showed that the anti-interference ability of PISM-DS system was stronger than DS system when the band-width, messaging rates and signal-to-noise ratio were same.